In order to recognize 2-dimensional codes, which have been obtained as a result of photographing, by making use of a special code reader, the edges of the image obtained as a result of the photographing must be clear and blurring must be sufficiently little. Due to restrictions imposed on the imaging system and due to the photographing environments, however, it is difficult to obtain an image with little blurring. In order to solve this problem, it is necessary to obtain an image with, whose blurring has been removed by carrying out image processing, as a recovered image.
For example, Patent Document 1 describes an image recovering method for eliminating blurring by adoption of a general image recovering technology for a 2-dimensional code area in an image. The image recovering method described in Patent Document 1 is carried out by execution of filtering on image data in order to provide a recovered image. In this case, the filtering is executed by making use of a blur eliminating filter for an image and an averaging filter of an edge holding type and an average type.
In addition, Patent Document 2 describes an image processing apparatus for eliminating blurring under a condition requiring that the image be a binary image. The image processing apparatus described in Patent Document 2 finds a correction quantity in order to provide an inferred image on the basis of the correction quantity. In this case, the correction quantity is found by integrating a correction quantity for binary conversion and a correction quantity for image deteriorations.
It is to be noted that, in the following description, the smallest unit of 2-dimensional codes is referred to as a cell. The case of a QR code (a registered trademark) is explained as an example by referring to FIG. 13. FIG. 13 is an explanatory diagram showing a QR code. White square points F131 composing the QR code shown in FIG. 13 are each a cell. In addition, a pattern used for detecting the position and size of the 2-dimensional code is referred to as a marker. In the QR code shown in FIG. 13, 3 corner square cut-out symbols are each a marker. The cut-out symbols are denoted by reference notations F132, F133 and F134. In addition, in the following description, an image of photographed 2-dimensional codes is referred to as a code image. Furthermore, an image with unclear edges is also referred to as a blurring image. Moreover, a 2-dimensional code is also referred to simply as a code in some cases.